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<h1 id="_1">对象</h1>
<h3 id="_2">初体验</h3>
<h4 id="_3">基本参数绑定</h4>
<div class="language-java highlight"><pre><span></span><code><span id="__span-0-1"><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-0-2"><a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-0-3"><a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Person</span><span class="p">();</span>
</span><span id="__span-0-4"><a id="__codelineno-0-4" name="__codelineno-0-4" href="#__codelineno-0-4"></a><span class="w">        </span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">15</span><span class="p">;</span><span class="w"> </span><span class="c1">// n的值为15</span>
</span><span id="__span-0-5"><a id="__codelineno-0-5" name="__codelineno-0-5" href="#__codelineno-0-5"></a><span class="w">        </span><span class="n">p</span><span class="p">.</span><span class="na">setAge</span><span class="p">(</span><span class="n">n</span><span class="p">);</span><span class="w"> </span><span class="c1">// 传入n的值</span>
</span><span id="__span-0-6"><a id="__codelineno-0-6" name="__codelineno-0-6" href="#__codelineno-0-6"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="na">getAge</span><span class="p">());</span><span class="w"> </span><span class="c1">// 15</span>
</span><span id="__span-0-7"><a id="__codelineno-0-7" name="__codelineno-0-7" href="#__codelineno-0-7"></a><span class="w">        </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">20</span><span class="p">;</span><span class="w"> </span><span class="c1">// n的值改为20</span>
</span><span id="__span-0-8"><a id="__codelineno-0-8" name="__codelineno-0-8" href="#__codelineno-0-8"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="na">getAge</span><span class="p">());</span><span class="w"> </span><span class="c1">// 15还是20?</span>
</span><span id="__span-0-9"><a id="__codelineno-0-9" name="__codelineno-0-9" href="#__codelineno-0-9"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-0-10"><a id="__codelineno-0-10" name="__codelineno-0-10" href="#__codelineno-0-10"></a><span class="p">}</span>
</span><span id="__span-0-11"><a id="__codelineno-0-11" name="__codelineno-0-11" href="#__codelineno-0-11"></a>
</span><span id="__span-0-12"><a id="__codelineno-0-12" name="__codelineno-0-12" href="#__codelineno-0-12"></a><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-0-13"><a id="__codelineno-0-13" name="__codelineno-0-13" href="#__codelineno-0-13"></a><span class="w">    </span><span class="kd">private</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">;</span>
</span><span id="__span-0-14"><a id="__codelineno-0-14" name="__codelineno-0-14" href="#__codelineno-0-14"></a>
</span><span id="__span-0-15"><a id="__codelineno-0-15" name="__codelineno-0-15" href="#__codelineno-0-15"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">getAge</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-0-16"><a id="__codelineno-0-16" name="__codelineno-0-16" href="#__codelineno-0-16"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">age</span><span class="p">;</span>
</span><span id="__span-0-17"><a id="__codelineno-0-17" name="__codelineno-0-17" href="#__codelineno-0-17"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-0-18"><a id="__codelineno-0-18" name="__codelineno-0-18" href="#__codelineno-0-18"></a>
</span><span id="__span-0-19"><a id="__codelineno-0-19" name="__codelineno-0-19" href="#__codelineno-0-19"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">setAge</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-0-20"><a id="__codelineno-0-20" name="__codelineno-0-20" href="#__codelineno-0-20"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">age</span><span class="p">;</span>
</span><span id="__span-0-21"><a id="__codelineno-0-21" name="__codelineno-0-21" href="#__codelineno-0-21"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-0-22"><a id="__codelineno-0-22" name="__codelineno-0-22" href="#__codelineno-0-22"></a><span class="p">}</span>
</span></code></pre></div>
<h4 id="_4">引用参数绑定</h4>
<div class="language-java highlight"><pre><span></span><code><span id="__span-1-1"><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-1-2"><a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-1-3"><a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Person</span><span class="p">();</span>
</span><span id="__span-1-4"><a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a><span class="w">        </span><span class="n">String</span><span class="w"> </span><span class="n">bob</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Bob&quot;</span><span class="p">;</span>
</span><span id="__span-1-5"><a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="w">        </span><span class="n">p</span><span class="p">.</span><span class="na">setName</span><span class="p">(</span><span class="n">bob</span><span class="p">);</span><span class="w"> </span><span class="c1">// 传入bob变量</span>
</span><span id="__span-1-6"><a id="__codelineno-1-6" name="__codelineno-1-6" href="#__codelineno-1-6"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="na">getName</span><span class="p">());</span><span class="w"> </span><span class="c1">// &quot;Bob&quot;</span>
</span><span id="__span-1-7"><a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="w">        </span><span class="n">bob</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Alice&quot;</span><span class="p">;</span><span class="w"> </span><span class="c1">// bob改名为Alice</span>
</span><span id="__span-1-8"><a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="na">getName</span><span class="p">());</span><span class="w"> </span><span class="c1">// &quot;Bob&quot;还是&quot;Alice&quot;?</span>
</span><span id="__span-1-9"><a id="__codelineno-1-9" name="__codelineno-1-9" href="#__codelineno-1-9"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-1-10"><a id="__codelineno-1-10" name="__codelineno-1-10" href="#__codelineno-1-10"></a><span class="p">}</span>
</span><span id="__span-1-11"><a id="__codelineno-1-11" name="__codelineno-1-11" href="#__codelineno-1-11"></a>
</span><span id="__span-1-12"><a id="__codelineno-1-12" name="__codelineno-1-12" href="#__codelineno-1-12"></a><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-1-13"><a id="__codelineno-1-13" name="__codelineno-1-13" href="#__codelineno-1-13"></a><span class="w">    </span><span class="kd">private</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-1-14"><a id="__codelineno-1-14" name="__codelineno-1-14" href="#__codelineno-1-14"></a>
</span><span id="__span-1-15"><a id="__codelineno-1-15" name="__codelineno-1-15" href="#__codelineno-1-15"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-1-16"><a id="__codelineno-1-16" name="__codelineno-1-16" href="#__codelineno-1-16"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="p">;</span>
</span><span id="__span-1-17"><a id="__codelineno-1-17" name="__codelineno-1-17" href="#__codelineno-1-17"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-1-18"><a id="__codelineno-1-18" name="__codelineno-1-18" href="#__codelineno-1-18"></a>
</span><span id="__span-1-19"><a id="__codelineno-1-19" name="__codelineno-1-19" href="#__codelineno-1-19"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">setName</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-1-20"><a id="__codelineno-1-20" name="__codelineno-1-20" href="#__codelineno-1-20"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-1-21"><a id="__codelineno-1-21" name="__codelineno-1-21" href="#__codelineno-1-21"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-1-22"><a id="__codelineno-1-22" name="__codelineno-1-22" href="#__codelineno-1-22"></a><span class="p">}</span>
</span></code></pre></div>
<h4 id="_5">综合使用</h4>
<p>引用绑定参数和构造方法method,并在主函数中调用</p>
<div class="language-java highlight"><pre><span></span><code><span id="__span-2-1"><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-2-2"><a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-2-3"><a id="__codelineno-2-3" name="__codelineno-2-3" href="#__codelineno-2-3"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Person</span><span class="p">(</span><span class="s">&quot;Xiao Ming&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p">);</span>
</span><span id="__span-2-4"><a id="__codelineno-2-4" name="__codelineno-2-4" href="#__codelineno-2-4"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="na">getName</span><span class="p">());</span><span class="w"> </span><span class="c1">//调用method</span>
</span><span id="__span-2-5"><a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="na">getAge</span><span class="p">());</span>
</span><span id="__span-2-6"><a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-2-7"><a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></a><span class="p">}</span>
</span><span id="__span-2-8"><a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a>
</span><span id="__span-2-9"><a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a>
</span><span id="__span-2-10"><a id="__codelineno-2-10" name="__codelineno-2-10" href="#__codelineno-2-10"></a><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-2-11"><a id="__codelineno-2-11" name="__codelineno-2-11" href="#__codelineno-2-11"></a><span class="w">    </span><span class="kd">private</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">;</span><span class="c1">// 默认值为null，可初始化</span>
</span><span id="__span-2-12"><a id="__codelineno-2-12" name="__codelineno-2-12" href="#__codelineno-2-12"></a><span class="w">    </span><span class="kd">private</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">;</span><span class="c1">// 默认值为0</span>
</span><span id="__span-2-13"><a id="__codelineno-2-13" name="__codelineno-2-13" href="#__codelineno-2-13"></a>
</span><span id="__span-2-14"><a id="__codelineno-2-14" name="__codelineno-2-14" href="#__codelineno-2-14"></a>
</span><span id="__span-2-15"><a id="__codelineno-2-15" name="__codelineno-2-15" href="#__codelineno-2-15"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="nf">Person</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w">  </span><span class="c1">// 默认构造方法，无参数，无执行语句，可与自定义构造函数一起使用</span>
</span><span id="__span-2-16"><a id="__codelineno-2-16" name="__codelineno-2-16" href="#__codelineno-2-16"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-2-17"><a id="__codelineno-2-17" name="__codelineno-2-17" href="#__codelineno-2-17"></a>
</span><span id="__span-2-18"><a id="__codelineno-2-18" name="__codelineno-2-18" href="#__codelineno-2-18"></a>
</span><span id="__span-2-19"><a id="__codelineno-2-19" name="__codelineno-2-19" href="#__codelineno-2-19"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="nf">Person</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="c1">// 自定义构造方法，有参数，有执行语句</span>
</span><span id="__span-2-20"><a id="__codelineno-2-20" name="__codelineno-2-20" href="#__codelineno-2-20"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-2-21"><a id="__codelineno-2-21" name="__codelineno-2-21" href="#__codelineno-2-21"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">age</span><span class="p">;</span><span class="w"> </span>
</span><span id="__span-2-22"><a id="__codelineno-2-22" name="__codelineno-2-22" href="#__codelineno-2-22"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-2-23"><a id="__codelineno-2-23" name="__codelineno-2-23" href="#__codelineno-2-23"></a>
</span><span id="__span-2-24"><a id="__codelineno-2-24" name="__codelineno-2-24" href="#__codelineno-2-24"></a><span class="w">        </span><span class="kd">public</span><span class="w"> </span><span class="nf">Person</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="c1">//本案例使用多构造方法</span>
</span><span id="__span-2-25"><a id="__codelineno-2-25" name="__codelineno-2-25" href="#__codelineno-2-25"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-2-26"><a id="__codelineno-2-26" name="__codelineno-2-26" href="#__codelineno-2-26"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">12</span><span class="p">;</span><span class="w">  </span><span class="c1">//在自定义构造函数中初始化age，以此为最终值</span>
</span><span id="__span-2-27"><a id="__codelineno-2-27" name="__codelineno-2-27" href="#__codelineno-2-27"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-2-28"><a id="__codelineno-2-28" name="__codelineno-2-28" href="#__codelineno-2-28"></a>
</span><span id="__span-2-29"><a id="__codelineno-2-29" name="__codelineno-2-29" href="#__codelineno-2-29"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-2-30"><a id="__codelineno-2-30" name="__codelineno-2-30" href="#__codelineno-2-30"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="p">;</span><span class="w"> </span><span class="c1">//构造方法中的执行语句</span>
</span><span id="__span-2-31"><a id="__codelineno-2-31" name="__codelineno-2-31" href="#__codelineno-2-31"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-2-32"><a id="__codelineno-2-32" name="__codelineno-2-32" href="#__codelineno-2-32"></a>
</span><span id="__span-2-33"><a id="__codelineno-2-33" name="__codelineno-2-33" href="#__codelineno-2-33"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">getAge</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-2-34"><a id="__codelineno-2-34" name="__codelineno-2-34" href="#__codelineno-2-34"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">age</span><span class="p">;</span>
</span><span id="__span-2-35"><a id="__codelineno-2-35" name="__codelineno-2-35" href="#__codelineno-2-35"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-2-36"><a id="__codelineno-2-36" name="__codelineno-2-36" href="#__codelineno-2-36"></a><span class="p">}</span>
</span></code></pre></div>
<h4 id="_6">方法重载</h4>
<div class="language-java highlight"><pre><span></span><code><span id="__span-3-1"><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a><span class="kd">class</span> <span class="nc">Hello</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-3-2"><a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">hello</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-3-3"><a id="__codelineno-3-3" name="__codelineno-3-3" href="#__codelineno-3-3"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Hello, world!&quot;</span><span class="p">);</span>
</span><span id="__span-3-4"><a id="__codelineno-3-4" name="__codelineno-3-4" href="#__codelineno-3-4"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-3-5"><a id="__codelineno-3-5" name="__codelineno-3-5" href="#__codelineno-3-5"></a>
</span><span id="__span-3-6"><a id="__codelineno-3-6" name="__codelineno-3-6" href="#__codelineno-3-6"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">hello</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-3-7"><a id="__codelineno-3-7" name="__codelineno-3-7" href="#__codelineno-3-7"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Hello, &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot;!&quot;</span><span class="p">);</span>
</span><span id="__span-3-8"><a id="__codelineno-3-8" name="__codelineno-3-8" href="#__codelineno-3-8"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-3-9"><a id="__codelineno-3-9" name="__codelineno-3-9" href="#__codelineno-3-9"></a>
</span><span id="__span-3-10"><a id="__codelineno-3-10" name="__codelineno-3-10" href="#__codelineno-3-10"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">hello</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-3-11"><a id="__codelineno-3-11" name="__codelineno-3-11" href="#__codelineno-3-11"></a><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">age</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">18</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-3-12"><a id="__codelineno-3-12" name="__codelineno-3-12" href="#__codelineno-3-12"></a><span class="w">            </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Hi, &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot;!&quot;</span><span class="p">);</span>
</span><span id="__span-3-13"><a id="__codelineno-3-13" name="__codelineno-3-13" href="#__codelineno-3-13"></a><span class="w">        </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-3-14"><a id="__codelineno-3-14" name="__codelineno-3-14" href="#__codelineno-3-14"></a><span class="w">            </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Hello, &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot;!&quot;</span><span class="p">);</span>
</span><span id="__span-3-15"><a id="__codelineno-3-15" name="__codelineno-3-15" href="#__codelineno-3-15"></a><span class="w">        </span><span class="p">}</span>
</span><span id="__span-3-16"><a id="__codelineno-3-16" name="__codelineno-3-16" href="#__codelineno-3-16"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-3-17"><a id="__codelineno-3-17" name="__codelineno-3-17" href="#__codelineno-3-17"></a><span class="p">}</span>
</span></code></pre></div>
<h4 id="_7">重载调用</h4>
<p>一是自定义，二是官方提供
<div class="language-java highlight"><pre><span></span><code><span id="__span-4-1"><a id="__codelineno-4-1" name="__codelineno-4-1" href="#__codelineno-4-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-4-2"><a id="__codelineno-4-2" name="__codelineno-4-2" href="#__codelineno-4-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-4-3"><a id="__codelineno-4-3" name="__codelineno-4-3" href="#__codelineno-4-3"></a><span class="w">        </span><span class="n">String</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Test string&quot;</span><span class="p">;</span>
</span><span id="__span-4-4"><a id="__codelineno-4-4" name="__codelineno-4-4" href="#__codelineno-4-4"></a><span class="w">        </span><span class="kt">int</span><span class="w"> </span><span class="n">n1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="na">indexOf</span><span class="p">(</span><span class="sc">&#39;t&#39;</span><span class="p">);</span><span class="c1">//int indexOf(int ch)：根据字符的Unicode码查找</span>
</span><span id="__span-4-5"><a id="__codelineno-4-5" name="__codelineno-4-5" href="#__codelineno-4-5"></a><span class="w">        </span><span class="kt">int</span><span class="w"> </span><span class="n">n2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="na">indexOf</span><span class="p">(</span><span class="s">&quot;st&quot;</span><span class="p">);</span><span class="c1">//int indexOf(String str)：根据字符串查找；</span>
</span><span id="__span-4-6"><a id="__codelineno-4-6" name="__codelineno-4-6" href="#__codelineno-4-6"></a><span class="w">        </span><span class="kt">int</span><span class="w"> </span><span class="n">n3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="na">indexOf</span><span class="p">(</span><span class="s">&quot;st&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">);</span><span class="c1">//根据字符串查找，但指定起始位置。</span>
</span><span id="__span-4-7"><a id="__codelineno-4-7" name="__codelineno-4-7" href="#__codelineno-4-7"></a><span class="w">        </span><span class="kt">int</span><span class="w"> </span><span class="n">n4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="na">indexOf</span><span class="p">(</span><span class="s">&quot;t&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">);</span><span class="c1">//根据字符查找，指定起始位置2,输出略</span>
</span><span id="__span-4-8"><a id="__codelineno-4-8" name="__codelineno-4-8" href="#__codelineno-4-8"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">n1</span><span class="p">);</span>
</span><span id="__span-4-9"><a id="__codelineno-4-9" name="__codelineno-4-9" href="#__codelineno-4-9"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">n2</span><span class="p">);</span>
</span><span id="__span-4-10"><a id="__codelineno-4-10" name="__codelineno-4-10" href="#__codelineno-4-10"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">n3</span><span class="p">);</span>
</span><span id="__span-4-11"><a id="__codelineno-4-11" name="__codelineno-4-11" href="#__codelineno-4-11"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">n4</span><span class="p">);</span>
</span><span id="__span-4-12"><a id="__codelineno-4-12" name="__codelineno-4-12" href="#__codelineno-4-12"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-4-13"><a id="__codelineno-4-13" name="__codelineno-4-13" href="#__codelineno-4-13"></a><span class="p">}</span>
</span></code></pre></div></p>
<h3 id="_8">继承</h3>
<p>我们让Student从Person继承时，Student就获得了Person的所有功能，我们只需要为Student编写新增的功能。
Java使用extends关键字来实现继承</p>
<p><div class="language-java highlight"><pre><span></span><code><span id="__span-5-1"><a id="__codelineno-5-1" name="__codelineno-5-1" href="#__codelineno-5-1"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-5-2"><a id="__codelineno-5-2" name="__codelineno-5-2" href="#__codelineno-5-2"></a><span class="w">    </span><span class="c1">// 不要重复name和age字段/方法,</span>
</span><span id="__span-5-3"><a id="__codelineno-5-3" name="__codelineno-5-3" href="#__codelineno-5-3"></a><span class="w">    </span><span class="c1">// 只需要定义新增score字段/方法:</span>
</span><span id="__span-5-4"><a id="__codelineno-5-4" name="__codelineno-5-4" href="#__codelineno-5-4"></a><span class="w">    </span><span class="kd">private</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">score</span><span class="p">;</span>
</span><span id="__span-5-5"><a id="__codelineno-5-5" name="__codelineno-5-5" href="#__codelineno-5-5"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">getScore</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="err">…</span><span class="w"> </span><span class="p">}</span>
</span><span id="__span-5-6"><a id="__codelineno-5-6" name="__codelineno-5-6" href="#__codelineno-5-6"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">setScore</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">score</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="err">…</span><span class="w"> </span><span class="p">}</span>
</span><span id="__span-5-7"><a id="__codelineno-5-7" name="__codelineno-5-7" href="#__codelineno-5-7"></a><span class="p">}</span>
</span></code></pre></div>
注意:因为在Java中，任何class的构造方法，第一行语句必须是调用父类的构造方法。如果没有明确地调用父类的构造方法，编译器会帮我们自动加一句super();，所以，Student类的构造方法实际上是这样：
<div class="language-java highlight"><pre><span></span><code><span id="__span-6-1"><a id="__codelineno-6-1" name="__codelineno-6-1" href="#__codelineno-6-1"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-6-2"><a id="__codelineno-6-2" name="__codelineno-6-2" href="#__codelineno-6-2"></a><span class="w">    </span><span class="kd">protected</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">score</span><span class="p">;</span>
</span><span id="__span-6-3"><a id="__codelineno-6-3" name="__codelineno-6-3" href="#__codelineno-6-3"></a>
</span><span id="__span-6-4"><a id="__codelineno-6-4" name="__codelineno-6-4" href="#__codelineno-6-4"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="nf">Student</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">score</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-6-5"><a id="__codelineno-6-5" name="__codelineno-6-5" href="#__codelineno-6-5"></a><span class="w">        </span><span class="kd">super</span><span class="p">();</span><span class="w"> </span><span class="c1">// 自动调用父类的构造方法</span>
</span><span id="__span-6-6"><a id="__codelineno-6-6" name="__codelineno-6-6" href="#__codelineno-6-6"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">score</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">score</span><span class="p">;</span>
</span><span id="__span-6-7"><a id="__codelineno-6-7" name="__codelineno-6-7" href="#__codelineno-6-7"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-6-8"><a id="__codelineno-6-8" name="__codelineno-6-8" href="#__codelineno-6-8"></a><span class="p">}</span>
</span></code></pre></div>
但是，Person类并没有无参数的构造方法，因此，编译失败。</p>
<p>解决方法是调用Person类存在的某个构造方法。例如：
<div class="language-java highlight"><pre><span></span><code><span id="__span-7-1"><a id="__codelineno-7-1" name="__codelineno-7-1" href="#__codelineno-7-1"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-7-2"><a id="__codelineno-7-2" name="__codelineno-7-2" href="#__codelineno-7-2"></a><span class="w">    </span><span class="kd">protected</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">score</span><span class="p">;</span>
</span><span id="__span-7-3"><a id="__codelineno-7-3" name="__codelineno-7-3" href="#__codelineno-7-3"></a>
</span><span id="__span-7-4"><a id="__codelineno-7-4" name="__codelineno-7-4" href="#__codelineno-7-4"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="nf">Student</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">score</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-7-5"><a id="__codelineno-7-5" name="__codelineno-7-5" href="#__codelineno-7-5"></a><span class="w">        </span><span class="kd">super</span><span class="p">(</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">age</span><span class="p">);</span><span class="w"> </span><span class="c1">// 调用父类的构造方法Person(String, int)</span>
</span><span id="__span-7-6"><a id="__codelineno-7-6" name="__codelineno-7-6" href="#__codelineno-7-6"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">score</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">score</span><span class="p">;</span>
</span><span id="__span-7-7"><a id="__codelineno-7-7" name="__codelineno-7-7" href="#__codelineno-7-7"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-7-8"><a id="__codelineno-7-8" name="__codelineno-7-8" href="#__codelineno-7-8"></a><span class="p">}</span>
</span></code></pre></div></p>
<h3 id="_9">多态</h3>
<p>在继承关系中，子类如果定义了一个与父类方法签名完全相同的方法，被称为覆写（Override）。
Override和Overload不同的是，如果方法签名不同，就是Overload，Overload方法是一个新方法；如果方法签名相同，并且返回值也相同，就是Override。
<div class="language-java highlight"><pre><span></span><code><span id="__span-8-1"><a id="__codelineno-8-1" name="__codelineno-8-1" href="#__codelineno-8-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-2"><a id="__codelineno-8-2" name="__codelineno-8-2" href="#__codelineno-8-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-3"><a id="__codelineno-8-3" name="__codelineno-8-3" href="#__codelineno-8-3"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Student</span><span class="p">();</span><span class="w">  </span><span class="c1">//继承</span>
</span><span id="__span-8-4"><a id="__codelineno-8-4" name="__codelineno-8-4" href="#__codelineno-8-4"></a><span class="w">        </span><span class="n">p</span><span class="p">.</span><span class="na">run</span><span class="p">();</span><span class="w"> </span><span class="c1">// 应该打印Person.run还是Student.run?</span>
</span><span id="__span-8-5"><a id="__codelineno-8-5" name="__codelineno-8-5" href="#__codelineno-8-5"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="na">hello</span><span class="p">());</span>
</span><span id="__span-8-6"><a id="__codelineno-8-6" name="__codelineno-8-6" href="#__codelineno-8-6"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-8-7"><a id="__codelineno-8-7" name="__codelineno-8-7" href="#__codelineno-8-7"></a><span class="p">}</span>
</span><span id="__span-8-8"><a id="__codelineno-8-8" name="__codelineno-8-8" href="#__codelineno-8-8"></a>
</span><span id="__span-8-9"><a id="__codelineno-8-9" name="__codelineno-8-9" href="#__codelineno-8-9"></a><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-10"><a id="__codelineno-8-10" name="__codelineno-8-10" href="#__codelineno-8-10"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-11"><a id="__codelineno-8-11" name="__codelineno-8-11" href="#__codelineno-8-11"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Person.run&quot;</span><span class="p">);</span>
</span><span id="__span-8-12"><a id="__codelineno-8-12" name="__codelineno-8-12" href="#__codelineno-8-12"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-8-13"><a id="__codelineno-8-13" name="__codelineno-8-13" href="#__codelineno-8-13"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">hello</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-14"><a id="__codelineno-8-14" name="__codelineno-8-14" href="#__codelineno-8-14"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="s">&quot;Hell&quot;</span><span class="p">;</span>
</span><span id="__span-8-15"><a id="__codelineno-8-15" name="__codelineno-8-15" href="#__codelineno-8-15"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-8-16"><a id="__codelineno-8-16" name="__codelineno-8-16" href="#__codelineno-8-16"></a><span class="p">}</span>
</span><span id="__span-8-17"><a id="__codelineno-8-17" name="__codelineno-8-17" href="#__codelineno-8-17"></a>
</span><span id="__span-8-18"><a id="__codelineno-8-18" name="__codelineno-8-18" href="#__codelineno-8-18"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-19"><a id="__codelineno-8-19" name="__codelineno-8-19" href="#__codelineno-8-19"></a><span class="w">    </span><span class="nd">@Override</span>
</span><span id="__span-8-20"><a id="__codelineno-8-20" name="__codelineno-8-20" href="#__codelineno-8-20"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-21"><a id="__codelineno-8-21" name="__codelineno-8-21" href="#__codelineno-8-21"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Student.run&quot;</span><span class="p">);</span>
</span><span id="__span-8-22"><a id="__codelineno-8-22" name="__codelineno-8-22" href="#__codelineno-8-22"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-8-23"><a id="__codelineno-8-23" name="__codelineno-8-23" href="#__codelineno-8-23"></a>
</span><span id="__span-8-24"><a id="__codelineno-8-24" name="__codelineno-8-24" href="#__codelineno-8-24"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">hello</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-8-25"><a id="__codelineno-8-25" name="__codelineno-8-25" href="#__codelineno-8-25"></a><span class="w">        </span><span class="c1">// 调用父类的hello()方法:</span>
</span><span id="__span-8-26"><a id="__codelineno-8-26" name="__codelineno-8-26" href="#__codelineno-8-26"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="kd">super</span><span class="p">.</span><span class="na">hello</span><span class="p">()</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot;!&quot;</span><span class="p">;</span>
</span><span id="__span-8-27"><a id="__codelineno-8-27" name="__codelineno-8-27" href="#__codelineno-8-27"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-8-28"><a id="__codelineno-8-28" name="__codelineno-8-28" href="#__codelineno-8-28"></a><span class="p">}</span>
</span></code></pre></div>
运行一下上面的代码就可以知道，实际上调用的方法是Student的run()方法。因此可得出结论：
Java的实例方法调用是基于运行时的实际类型的动态调用，而非变量的声明类型。
这个非常重要的特性在面向对象编程中称之为多态。它的英文拼写非常复杂：Polymorphic。</p>
<h4 id="super">super</h4>
<p>在子类的覆写方法中，如果要调用父类的被覆写的方法，可以通过super来调用。这段代码就调用了父类的hello()方法，所以打印出Hell!
<div class="language-java highlight"><pre><span></span><code><span id="__span-9-1"><a id="__codelineno-9-1" name="__codelineno-9-1" href="#__codelineno-9-1"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">hello</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-9-2"><a id="__codelineno-9-2" name="__codelineno-9-2" href="#__codelineno-9-2"></a><span class="w">        </span><span class="c1">// 调用父类的hello()方法:</span>
</span><span id="__span-9-3"><a id="__codelineno-9-3" name="__codelineno-9-3" href="#__codelineno-9-3"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="kd">super</span><span class="p">.</span><span class="na">hello</span><span class="p">()</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot;!&quot;</span><span class="p">;</span>
</span><span id="__span-9-4"><a id="__codelineno-9-4" name="__codelineno-9-4" href="#__codelineno-9-4"></a><span class="w">    </span><span class="p">}</span>
</span></code></pre></div></p>
<h4 id="final">final</h4>
<p>继承可以允许子类覆写父类的方法。如果一个父类不允许子类对它的某个方法进行覆写，可以把该方法标记为final。用final修饰的方法不能被Override。</p>
<h4 id="_10">抽象</h4>
<p>如果父类的方法本身不需要实现任何功能，仅仅是为了定义方法签名，目的是让子类去覆写它，那么，可以把父类的方法声明为抽象方法：
<div class="language-java highlight"><pre><span></span><code><span id="__span-10-1"><a id="__codelineno-10-1" name="__codelineno-10-1" href="#__codelineno-10-1"></a><span class="kd">abstract</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-10-2"><a id="__codelineno-10-2" name="__codelineno-10-2" href="#__codelineno-10-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">abstract</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">();</span>
</span><span id="__span-10-3"><a id="__codelineno-10-3" name="__codelineno-10-3" href="#__codelineno-10-3"></a><span class="p">}</span>
</span></code></pre></div>
把一个方法声明为<code>abstract</code>，表示它是一个抽象方法，本身没有实现任何方法语句.
编译器会告诉我们，无法编译Person类，因为它包含抽象方法。必须把Person类本身也声明为abstract，才能正确编译它,使用abstract修饰的类就是抽象类。我们<code>无法实例化一个抽象类</code>：
<div class="language-java highlight"><pre><span></span><code><span id="__span-11-1"><a id="__codelineno-11-1" name="__codelineno-11-1" href="#__codelineno-11-1"></a><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Person</span><span class="p">();</span><span class="w"> </span><span class="c1">// 编译错误</span>
</span></code></pre></div>
无法实例化的抽象类有什么用？
因为抽象类本身被设计成<code>只能用于被继承</code>，因此，抽象类可以强迫子类实现其定义的抽象方法，否则编译会报错。因此，抽象方法实际上相当于定义了“<code>规范</code>”.例如，Person类定义了抽象方法run()，那么，在实现子类Student的时候，就必须覆写run()方法
<div class="language-java highlight"><pre><span></span><code><span id="__span-12-1"><a id="__codelineno-12-1" name="__codelineno-12-1" href="#__codelineno-12-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-12-2"><a id="__codelineno-12-2" name="__codelineno-12-2" href="#__codelineno-12-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-12-3"><a id="__codelineno-12-3" name="__codelineno-12-3" href="#__codelineno-12-3"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Student</span><span class="p">();</span>
</span><span id="__span-12-4"><a id="__codelineno-12-4" name="__codelineno-12-4" href="#__codelineno-12-4"></a><span class="w">        </span><span class="n">p</span><span class="p">.</span><span class="na">run</span><span class="p">();</span>
</span><span id="__span-12-5"><a id="__codelineno-12-5" name="__codelineno-12-5" href="#__codelineno-12-5"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-12-6"><a id="__codelineno-12-6" name="__codelineno-12-6" href="#__codelineno-12-6"></a><span class="p">}</span>
</span><span id="__span-12-7"><a id="__codelineno-12-7" name="__codelineno-12-7" href="#__codelineno-12-7"></a>
</span><span id="__span-12-8"><a id="__codelineno-12-8" name="__codelineno-12-8" href="#__codelineno-12-8"></a><span class="kd">abstract</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-12-9"><a id="__codelineno-12-9" name="__codelineno-12-9" href="#__codelineno-12-9"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">abstract</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">();</span>
</span><span id="__span-12-10"><a id="__codelineno-12-10" name="__codelineno-12-10" href="#__codelineno-12-10"></a><span class="p">}</span>
</span><span id="__span-12-11"><a id="__codelineno-12-11" name="__codelineno-12-11" href="#__codelineno-12-11"></a>
</span><span id="__span-12-12"><a id="__codelineno-12-12" name="__codelineno-12-12" href="#__codelineno-12-12"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-12-13"><a id="__codelineno-12-13" name="__codelineno-12-13" href="#__codelineno-12-13"></a><span class="w">    </span><span class="nd">@Override</span>
</span><span id="__span-12-14"><a id="__codelineno-12-14" name="__codelineno-12-14" href="#__codelineno-12-14"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-12-15"><a id="__codelineno-12-15" name="__codelineno-12-15" href="#__codelineno-12-15"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Student.run&quot;</span><span class="p">);</span>
</span><span id="__span-12-16"><a id="__codelineno-12-16" name="__codelineno-12-16" href="#__codelineno-12-16"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-12-17"><a id="__codelineno-12-17" name="__codelineno-12-17" href="#__codelineno-12-17"></a><span class="p">}</span>
</span></code></pre></div>
所以使用父类方法名即可调用子类中方法，无需关注子类中再次重写的父类方法。
这种尽<code>量引用高层类型，避免引用实际子类型</code>的方式，称之为面向抽象编程
<code>不需要子类</code>就可以实现业务逻辑（正常编译），具体的业务逻辑由不同的子类实现，调用者并不关心</p>
<h4 id="_11">接口</h4>
<p>在抽象类中，抽象方法本质上是定义接口规范：即规定高层类的接口，从而保证所有子类都有相同的接口实现，更多实现面向抽象编程</p>
<p>如果一个抽象类没有字段，所有方法全部都是抽象方法：
<div class="language-java highlight"><pre><span></span><code><span id="__span-13-1"><a id="__codelineno-13-1" name="__codelineno-13-1" href="#__codelineno-13-1"></a><span class="kd">abstract</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-13-2"><a id="__codelineno-13-2" name="__codelineno-13-2" href="#__codelineno-13-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">abstract</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">();</span>
</span><span id="__span-13-3"><a id="__codelineno-13-3" name="__codelineno-13-3" href="#__codelineno-13-3"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">abstract</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">();</span>
</span><span id="__span-13-4"><a id="__codelineno-13-4" name="__codelineno-13-4" href="#__codelineno-13-4"></a><span class="p">}</span>
</span></code></pre></div>
就可以把该抽象类改写为接口：interface。</p>
<p>在Java中，使用interface可以声明一个接口：
<div class="language-java highlight"><pre><span></span><code><span id="__span-14-1"><a id="__codelineno-14-1" name="__codelineno-14-1" href="#__codelineno-14-1"></a><span class="kd">interface</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-14-2"><a id="__codelineno-14-2" name="__codelineno-14-2" href="#__codelineno-14-2"></a><span class="w">    </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">();</span>
</span><span id="__span-14-3"><a id="__codelineno-14-3" name="__codelineno-14-3" href="#__codelineno-14-3"></a><span class="w">    </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">();</span>
</span><span id="__span-14-4"><a id="__codelineno-14-4" name="__codelineno-14-4" href="#__codelineno-14-4"></a><span class="p">}</span>
</span></code></pre></div></p>
<h5 id="_12">接口使用</h5>
<p><code>interface</code>就是比抽象类还要抽象的纯抽象接口，因为它连字段都不能有。因为接口定义的所有方法默认都是<code>public abstract</code>的，所以这两个修饰符不需要写出来。
当一个具体的<code>class</code>去实现一个<code>interface</code>时，需要使用<code>implements</code>关键字。举个例子：
<div class="language-java highlight"><pre><span></span><code><span id="__span-15-1"><a id="__codelineno-15-1" name="__codelineno-15-1" href="#__codelineno-15-1"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">implements</span><span class="w"> </span><span class="n">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-15-2"><a id="__codelineno-15-2" name="__codelineno-15-2" href="#__codelineno-15-2"></a><span class="w">    </span><span class="kd">private</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-15-3"><a id="__codelineno-15-3" name="__codelineno-15-3" href="#__codelineno-15-3"></a>
</span><span id="__span-15-4"><a id="__codelineno-15-4" name="__codelineno-15-4" href="#__codelineno-15-4"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="nf">Student</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-15-5"><a id="__codelineno-15-5" name="__codelineno-15-5" href="#__codelineno-15-5"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-15-6"><a id="__codelineno-15-6" name="__codelineno-15-6" href="#__codelineno-15-6"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-15-7"><a id="__codelineno-15-7" name="__codelineno-15-7" href="#__codelineno-15-7"></a>
</span><span id="__span-15-8"><a id="__codelineno-15-8" name="__codelineno-15-8" href="#__codelineno-15-8"></a><span class="w">    </span><span class="nd">@Override</span>
</span><span id="__span-15-9"><a id="__codelineno-15-9" name="__codelineno-15-9" href="#__codelineno-15-9"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-15-10"><a id="__codelineno-15-10" name="__codelineno-15-10" href="#__codelineno-15-10"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot; run&quot;</span><span class="p">);</span>
</span><span id="__span-15-11"><a id="__codelineno-15-11" name="__codelineno-15-11" href="#__codelineno-15-11"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-15-12"><a id="__codelineno-15-12" name="__codelineno-15-12" href="#__codelineno-15-12"></a>
</span><span id="__span-15-13"><a id="__codelineno-15-13" name="__codelineno-15-13" href="#__codelineno-15-13"></a><span class="w">    </span><span class="nd">@Override</span>
</span><span id="__span-15-14"><a id="__codelineno-15-14" name="__codelineno-15-14" href="#__codelineno-15-14"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-15-15"><a id="__codelineno-15-15" name="__codelineno-15-15" href="#__codelineno-15-15"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="p">;</span>
</span><span id="__span-15-16"><a id="__codelineno-15-16" name="__codelineno-15-16" href="#__codelineno-15-16"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-15-17"><a id="__codelineno-15-17" name="__codelineno-15-17" href="#__codelineno-15-17"></a><span class="p">}</span>
</span></code></pre></div>
在Java中，一个类只能继承自另一个类，不能从多个类继承。但是，一个类可以实现多个<code>interface</code>，例如：
<div class="language-java highlight"><pre><span></span><code><span id="__span-16-1"><a id="__codelineno-16-1" name="__codelineno-16-1" href="#__codelineno-16-1"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">implements</span><span class="w"> </span><span class="n">Person</span><span class="p">,</span><span class="n">knowledge</span><span class="w"> </span><span class="c1">// 实现了两个interface</span>
</span></code></pre></div></p>
<h5 id="_13">接口继承</h5>
<p>一个interface可以继承自另一个interface。interface继承自interface使用<code>extends</code>，它相当于扩展了接口的方法。例如：
<div class="language-java highlight"><pre><span></span><code><span id="__span-17-1"><a id="__codelineno-17-1" name="__codelineno-17-1" href="#__codelineno-17-1"></a><span class="kd">interface</span> <span class="nc">Hello</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-17-2"><a id="__codelineno-17-2" name="__codelineno-17-2" href="#__codelineno-17-2"></a><span class="w">    </span><span class="kt">void</span><span class="w"> </span><span class="nf">hello</span><span class="p">();</span>
</span><span id="__span-17-3"><a id="__codelineno-17-3" name="__codelineno-17-3" href="#__codelineno-17-3"></a><span class="p">}</span>
</span><span id="__span-17-4"><a id="__codelineno-17-4" name="__codelineno-17-4" href="#__codelineno-17-4"></a>
</span><span id="__span-17-5"><a id="__codelineno-17-5" name="__codelineno-17-5" href="#__codelineno-17-5"></a><span class="kd">interface</span> <span class="nc">Person</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Hello</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-17-6"><a id="__codelineno-17-6" name="__codelineno-17-6" href="#__codelineno-17-6"></a><span class="w">    </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">();</span>
</span><span id="__span-17-7"><a id="__codelineno-17-7" name="__codelineno-17-7" href="#__codelineno-17-7"></a><span class="w">    </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">();</span>
</span><span id="__span-17-8"><a id="__codelineno-17-8" name="__codelineno-17-8" href="#__codelineno-17-8"></a><span class="p">}</span>
</span></code></pre></div>
此时，<code>Person</code>接口继承自Hello接口，因此，Person接口现在实际上有3个<code>抽象方法签名</code>，其中一个来自继承的Hello接口</p>
<h4 id="_14">接口增加方法</h4>
<p>实现类可以不必覆写default方法。default方法的目的是，当我们需要给接口新增一个方法时，会涉及到修改全部子类。如果新增的是default方法，那么子类就不必全部修改，只需要在需要覆写的地方去覆写新增方法。
<div class="language-java highlight"><pre><span></span><code><span id="__span-18-1"><a id="__codelineno-18-1" name="__codelineno-18-1" href="#__codelineno-18-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-18-2"><a id="__codelineno-18-2" name="__codelineno-18-2" href="#__codelineno-18-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-18-3"><a id="__codelineno-18-3" name="__codelineno-18-3" href="#__codelineno-18-3"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Student</span><span class="p">(</span><span class="s">&quot;Xiao Ming&quot;</span><span class="p">);</span>
</span><span id="__span-18-4"><a id="__codelineno-18-4" name="__codelineno-18-4" href="#__codelineno-18-4"></a><span class="w">        </span><span class="n">p</span><span class="p">.</span><span class="na">run</span><span class="p">();</span>
</span><span id="__span-18-5"><a id="__codelineno-18-5" name="__codelineno-18-5" href="#__codelineno-18-5"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-18-6"><a id="__codelineno-18-6" name="__codelineno-18-6" href="#__codelineno-18-6"></a><span class="p">}</span>
</span><span id="__span-18-7"><a id="__codelineno-18-7" name="__codelineno-18-7" href="#__codelineno-18-7"></a>
</span><span id="__span-18-8"><a id="__codelineno-18-8" name="__codelineno-18-8" href="#__codelineno-18-8"></a><span class="kd">interface</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-18-9"><a id="__codelineno-18-9" name="__codelineno-18-9" href="#__codelineno-18-9"></a><span class="w">    </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">();</span>
</span><span id="__span-18-10"><a id="__codelineno-18-10" name="__codelineno-18-10" href="#__codelineno-18-10"></a><span class="w">    </span><span class="k">default</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-18-11"><a id="__codelineno-18-11" name="__codelineno-18-11" href="#__codelineno-18-11"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">getName</span><span class="p">()</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot; run&quot;</span><span class="p">);</span>
</span><span id="__span-18-12"><a id="__codelineno-18-12" name="__codelineno-18-12" href="#__codelineno-18-12"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-18-13"><a id="__codelineno-18-13" name="__codelineno-18-13" href="#__codelineno-18-13"></a><span class="p">}</span>
</span><span id="__span-18-14"><a id="__codelineno-18-14" name="__codelineno-18-14" href="#__codelineno-18-14"></a>
</span><span id="__span-18-15"><a id="__codelineno-18-15" name="__codelineno-18-15" href="#__codelineno-18-15"></a><span class="kd">class</span> <span class="nc">Student</span><span class="w"> </span><span class="kd">implements</span><span class="w"> </span><span class="n">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-18-16"><a id="__codelineno-18-16" name="__codelineno-18-16" href="#__codelineno-18-16"></a><span class="w">    </span><span class="kd">private</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-18-17"><a id="__codelineno-18-17" name="__codelineno-18-17" href="#__codelineno-18-17"></a>
</span><span id="__span-18-18"><a id="__codelineno-18-18" name="__codelineno-18-18" href="#__codelineno-18-18"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="nf">Student</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-18-19"><a id="__codelineno-18-19" name="__codelineno-18-19" href="#__codelineno-18-19"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-18-20"><a id="__codelineno-18-20" name="__codelineno-18-20" href="#__codelineno-18-20"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-18-21"><a id="__codelineno-18-21" name="__codelineno-18-21" href="#__codelineno-18-21"></a>
</span><span id="__span-18-22"><a id="__codelineno-18-22" name="__codelineno-18-22" href="#__codelineno-18-22"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">getName</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-18-23"><a id="__codelineno-18-23" name="__codelineno-18-23" href="#__codelineno-18-23"></a><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="p">;</span>
</span><span id="__span-18-24"><a id="__codelineno-18-24" name="__codelineno-18-24" href="#__codelineno-18-24"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-18-25"><a id="__codelineno-18-25" name="__codelineno-18-25" href="#__codelineno-18-25"></a><span class="p">}</span>
</span></code></pre></div></p>
<p>default方法和抽象类的普通方法是有所不同的。因为interface没有字段，default方法无法访问字段，而抽象类的普通方法可以访问实例字段。</p>
<h4 id="_15">静态字段和方法</h4>
<p>在一个class中定义的字段，我们称之为实例字段。实例字段的特点是，每个实例都有独立的字段，各个实例的同名字段互不影响。</p>
<p>还有一种字段，是用static修饰的字段，称为静态字段，定义<code>public static int 变量</code></p>
<p>实例字段在每个实例中都有自己的一个独立“空间”，但是静态字段只有一个共享“空间”，所有实例都会共享该字段。可以得到下面代码结果,可以理解"所有实例共享一个静态字段"吗
<div class="language-text highlight"><pre><span></span><code><span id="__span-19-1"><a id="__codelineno-19-1" name="__codelineno-19-1" href="#__codelineno-19-1"></a>88
</span><span id="__span-19-2"><a id="__codelineno-19-2" name="__codelineno-19-2" href="#__codelineno-19-2"></a>99
</span></code></pre></div>
<div class="language-java highlight"><pre><span></span><code><span id="__span-20-1"><a id="__codelineno-20-1" name="__codelineno-20-1" href="#__codelineno-20-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-20-2"><a id="__codelineno-20-2" name="__codelineno-20-2" href="#__codelineno-20-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-20-3"><a id="__codelineno-20-3" name="__codelineno-20-3" href="#__codelineno-20-3"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">ming</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Person</span><span class="p">(</span><span class="s">&quot;Xiao Ming&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">12</span><span class="p">);</span>
</span><span id="__span-20-4"><a id="__codelineno-20-4" name="__codelineno-20-4" href="#__codelineno-20-4"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">hong</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Person</span><span class="p">(</span><span class="s">&quot;Xiao Hong&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p">);</span>
</span><span id="__span-20-5"><a id="__codelineno-20-5" name="__codelineno-20-5" href="#__codelineno-20-5"></a><span class="w">        </span><span class="n">ming</span><span class="p">.</span><span class="na">number</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">88</span><span class="p">;</span>
</span><span id="__span-20-6"><a id="__codelineno-20-6" name="__codelineno-20-6" href="#__codelineno-20-6"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">hong</span><span class="p">.</span><span class="na">number</span><span class="p">);</span>
</span><span id="__span-20-7"><a id="__codelineno-20-7" name="__codelineno-20-7" href="#__codelineno-20-7"></a><span class="w">        </span><span class="n">hong</span><span class="p">.</span><span class="na">number</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">99</span><span class="p">;</span>
</span><span id="__span-20-8"><a id="__codelineno-20-8" name="__codelineno-20-8" href="#__codelineno-20-8"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">ming</span><span class="p">.</span><span class="na">number</span><span class="p">);</span>
</span><span id="__span-20-9"><a id="__codelineno-20-9" name="__codelineno-20-9" href="#__codelineno-20-9"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-20-10"><a id="__codelineno-20-10" name="__codelineno-20-10" href="#__codelineno-20-10"></a><span class="p">}</span>
</span><span id="__span-20-11"><a id="__codelineno-20-11" name="__codelineno-20-11" href="#__codelineno-20-11"></a>
</span><span id="__span-20-12"><a id="__codelineno-20-12" name="__codelineno-20-12" href="#__codelineno-20-12"></a><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-20-13"><a id="__codelineno-20-13" name="__codelineno-20-13" href="#__codelineno-20-13"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-20-14"><a id="__codelineno-20-14" name="__codelineno-20-14" href="#__codelineno-20-14"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">;</span>
</span><span id="__span-20-15"><a id="__codelineno-20-15" name="__codelineno-20-15" href="#__codelineno-20-15"></a>
</span><span id="__span-20-16"><a id="__codelineno-20-16" name="__codelineno-20-16" href="#__codelineno-20-16"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">number</span><span class="p">;</span>
</span><span id="__span-20-17"><a id="__codelineno-20-17" name="__codelineno-20-17" href="#__codelineno-20-17"></a>
</span><span id="__span-20-18"><a id="__codelineno-20-18" name="__codelineno-20-18" href="#__codelineno-20-18"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="nf">Person</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">age</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-20-19"><a id="__codelineno-20-19" name="__codelineno-20-19" href="#__codelineno-20-19"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">name</span><span class="p">;</span>
</span><span id="__span-20-20"><a id="__codelineno-20-20" name="__codelineno-20-20" href="#__codelineno-20-20"></a><span class="w">        </span><span class="k">this</span><span class="p">.</span><span class="na">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">age</span><span class="p">;</span>
</span><span id="__span-20-21"><a id="__codelineno-20-21" name="__codelineno-20-21" href="#__codelineno-20-21"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-20-22"><a id="__codelineno-20-22" name="__codelineno-20-22" href="#__codelineno-20-22"></a><span class="p">}</span>
</span></code></pre></div>
调用实例方法必须通过一个实例变量，而调用静态方法则不需要实例变量，通过类名就可以调用。静态方法类似其它编程语言的函数。（略）
<div class="language-java highlight"><pre><span></span><code><span id="__span-21-1"><a id="__codelineno-21-1" name="__codelineno-21-1" href="#__codelineno-21-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span><span class="w">  </span><span class="c1">//该例</span>
</span><span id="__span-21-2"><a id="__codelineno-21-2" name="__codelineno-21-2" href="#__codelineno-21-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-21-3"><a id="__codelineno-21-3" name="__codelineno-21-3" href="#__codelineno-21-3"></a><span class="w">        </span><span class="n">Person</span><span class="p">.</span><span class="na">setNumber</span><span class="p">(</span><span class="mi">99</span><span class="p">);</span><span class="w">  </span>
</span><span id="__span-21-4"><a id="__codelineno-21-4" name="__codelineno-21-4" href="#__codelineno-21-4"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="n">Person</span><span class="p">.</span><span class="na">number</span><span class="p">);</span>
</span><span id="__span-21-5"><a id="__codelineno-21-5" name="__codelineno-21-5" href="#__codelineno-21-5"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-21-6"><a id="__codelineno-21-6" name="__codelineno-21-6" href="#__codelineno-21-6"></a><span class="p">}</span>
</span><span id="__span-21-7"><a id="__codelineno-21-7" name="__codelineno-21-7" href="#__codelineno-21-7"></a>
</span><span id="__span-21-8"><a id="__codelineno-21-8" name="__codelineno-21-8" href="#__codelineno-21-8"></a><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-21-9"><a id="__codelineno-21-9" name="__codelineno-21-9" href="#__codelineno-21-9"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">number</span><span class="p">;</span>
</span><span id="__span-21-10"><a id="__codelineno-21-10" name="__codelineno-21-10" href="#__codelineno-21-10"></a>
</span><span id="__span-21-11"><a id="__codelineno-21-11" name="__codelineno-21-11" href="#__codelineno-21-11"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">setNumber</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">value</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-21-12"><a id="__codelineno-21-12" name="__codelineno-21-12" href="#__codelineno-21-12"></a><span class="w">        </span><span class="n">number</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">value</span><span class="p">;</span>
</span><span id="__span-21-13"><a id="__codelineno-21-13" name="__codelineno-21-13" href="#__codelineno-21-13"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-21-14"><a id="__codelineno-21-14" name="__codelineno-21-14" href="#__codelineno-21-14"></a><span class="p">}</span>
</span></code></pre></div></p>
<h4 id="_16">接口的静态方法</h4>
<p>因为interface是一个纯抽象类，所以它不能定义实例字段。但是，interface是可以有静态字段的，并且静态字段必须为final类型：
<div class="language-java highlight"><pre><span></span><code><span id="__span-22-1"><a id="__codelineno-22-1" name="__codelineno-22-1" href="#__codelineno-22-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">interface</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-22-2"><a id="__codelineno-22-2" name="__codelineno-22-2" href="#__codelineno-22-2"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kd">final</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">MALE</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
</span><span id="__span-22-3"><a id="__codelineno-22-3" name="__codelineno-22-3" href="#__codelineno-22-3"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kd">final</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">FEMALE</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span>
</span><span id="__span-22-4"><a id="__codelineno-22-4" name="__codelineno-22-4" href="#__codelineno-22-4"></a><span class="p">}</span>
</span></code></pre></div>
实际上，因为interface的字段只能是public static final类型，所以我们可以把这些修饰符都去掉，上述代码可以简写为：
<div class="language-java highlight"><pre><span></span><code><span id="__span-23-1"><a id="__codelineno-23-1" name="__codelineno-23-1" href="#__codelineno-23-1"></a><span class="kd">public</span><span class="w"> </span><span class="kd">interface</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-23-2"><a id="__codelineno-23-2" name="__codelineno-23-2" href="#__codelineno-23-2"></a><span class="w">    </span><span class="c1">// 编译器会自动加上public statc final:</span>
</span><span id="__span-23-3"><a id="__codelineno-23-3" name="__codelineno-23-3" href="#__codelineno-23-3"></a><span class="w">    </span><span class="kt">int</span><span class="w"> </span><span class="n">MALE</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
</span><span id="__span-23-4"><a id="__codelineno-23-4" name="__codelineno-23-4" href="#__codelineno-23-4"></a><span class="w">    </span><span class="kt">int</span><span class="w"> </span><span class="n">FEMALE</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span>
</span><span id="__span-23-5"><a id="__codelineno-23-5" name="__codelineno-23-5" href="#__codelineno-23-5"></a><span class="p">}</span>
</span></code></pre></div>
编译器会自动把该字段变为public static final类型。</p>
<h4 id="_17">导入类的静态字段和静态方法</h4>
<p>import static的语法，它可以导入一个类的静态字段和静态方法：
<div class="language-java highlight"><pre><span></span><code><span id="__span-24-1"><a id="__codelineno-24-1" name="__codelineno-24-1" href="#__codelineno-24-1"></a><span class="kn">package</span><span class="w"> </span><span class="nn">main</span><span class="p">;</span>
</span><span id="__span-24-2"><a id="__codelineno-24-2" name="__codelineno-24-2" href="#__codelineno-24-2"></a>
</span><span id="__span-24-3"><a id="__codelineno-24-3" name="__codelineno-24-3" href="#__codelineno-24-3"></a><span class="c1">// 导入System类的所有静态字段和静态方法:</span>
</span><span id="__span-24-4"><a id="__codelineno-24-4" name="__codelineno-24-4" href="#__codelineno-24-4"></a><span class="kn">import static</span><span class="w"> </span><span class="nn">java.lang.System.*</span><span class="p">;</span>
</span><span id="__span-24-5"><a id="__codelineno-24-5" name="__codelineno-24-5" href="#__codelineno-24-5"></a>
</span><span id="__span-24-6"><a id="__codelineno-24-6" name="__codelineno-24-6" href="#__codelineno-24-6"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-24-7"><a id="__codelineno-24-7" name="__codelineno-24-7" href="#__codelineno-24-7"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-24-8"><a id="__codelineno-24-8" name="__codelineno-24-8" href="#__codelineno-24-8"></a><span class="w">        </span><span class="c1">// 相当于调用System.out.println(…)</span>
</span><span id="__span-24-9"><a id="__codelineno-24-9" name="__codelineno-24-9" href="#__codelineno-24-9"></a><span class="w">        </span><span class="n">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Hello, world!&quot;</span><span class="p">);</span>
</span><span id="__span-24-10"><a id="__codelineno-24-10" name="__codelineno-24-10" href="#__codelineno-24-10"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-24-11"><a id="__codelineno-24-11" name="__codelineno-24-11" href="#__codelineno-24-11"></a><span class="p">}</span>
</span></code></pre></div>
import static很少使用</p>
<h3 id="_18">包</h3>
<p>ava定义了一种名字空间，称之为包：<code>package</code>。一个类总是属于某个包，类名（比如Person）只是一个简写，真正的完整类名是<code>包名.类名</code>
在定义class的时候，我们需要在第一行声明这个class属于哪个包。
如小明，小红和小军的Person.java文件，可以看到<code>mr.jun</code>多级包结构
<div class="language-java highlight"><pre><span></span><code><span id="__span-25-1"><a id="__codelineno-25-1" name="__codelineno-25-1" href="#__codelineno-25-1"></a><span class="kn">package</span><span class="w"> </span><span class="nn">ming</span><span class="p">;</span><span class="w"> </span><span class="c1">// 申明包名ming</span>
</span><span id="__span-25-2"><a id="__codelineno-25-2" name="__codelineno-25-2" href="#__codelineno-25-2"></a>
</span><span id="__span-25-3"><a id="__codelineno-25-3" name="__codelineno-25-3" href="#__codelineno-25-3"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-25-4"><a id="__codelineno-25-4" name="__codelineno-25-4" href="#__codelineno-25-4"></a><span class="p">}</span>
</span><span id="__span-25-5"><a id="__codelineno-25-5" name="__codelineno-25-5" href="#__codelineno-25-5"></a><span class="kn">package</span><span class="w"> </span><span class="nn">hong</span><span class="p">;</span><span class="w"> </span><span class="c1">// 申明包名ming</span>
</span><span id="__span-25-6"><a id="__codelineno-25-6" name="__codelineno-25-6" href="#__codelineno-25-6"></a>
</span><span id="__span-25-7"><a id="__codelineno-25-7" name="__codelineno-25-7" href="#__codelineno-25-7"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-25-8"><a id="__codelineno-25-8" name="__codelineno-25-8" href="#__codelineno-25-8"></a><span class="p">}</span>
</span><span id="__span-25-9"><a id="__codelineno-25-9" name="__codelineno-25-9" href="#__codelineno-25-9"></a><span class="kn">package</span><span class="w"> </span><span class="nn">mr.jun</span><span class="p">;</span><span class="w"> </span><span class="c1">// 申明包名mr.jun，包的多级结构</span>
</span><span id="__span-25-10"><a id="__codelineno-25-10" name="__codelineno-25-10" href="#__codelineno-25-10"></a>
</span><span id="__span-25-11"><a id="__codelineno-25-11" name="__codelineno-25-11" href="#__codelineno-25-11"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Arrays</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-25-12"><a id="__codelineno-25-12" name="__codelineno-25-12" href="#__codelineno-25-12"></a><span class="p">}</span>
</span></code></pre></div>
在生成字节码的时候文件结构是
<div class="language-text highlight"><pre><span></span><code><span id="__span-26-1"><a id="__codelineno-26-1" name="__codelineno-26-1" href="#__codelineno-26-1"></a> src
</span><span id="__span-26-2"><a id="__codelineno-26-2" name="__codelineno-26-2" href="#__codelineno-26-2"></a>    |- hong
</span><span id="__span-26-3"><a id="__codelineno-26-3" name="__codelineno-26-3" href="#__codelineno-26-3"></a>    │  └─ Person.java
</span><span id="__span-26-4"><a id="__codelineno-26-4" name="__codelineno-26-4" href="#__codelineno-26-4"></a>    |- ming
</span><span id="__span-26-5"><a id="__codelineno-26-5" name="__codelineno-26-5" href="#__codelineno-26-5"></a>    │  └─ Person.java
</span><span id="__span-26-6"><a id="__codelineno-26-6" name="__codelineno-26-6" href="#__codelineno-26-6"></a>    └─ mr
</span><span id="__span-26-7"><a id="__codelineno-26-7" name="__codelineno-26-7" href="#__codelineno-26-7"></a>       └─ jun
</span><span id="__span-26-8"><a id="__codelineno-26-8" name="__codelineno-26-8" href="#__codelineno-26-8"></a>          └─ Arrays.java
</span></code></pre></div>
编译后一样
<div class="language-text highlight"><pre><span></span><code><span id="__span-27-1"><a id="__codelineno-27-1" name="__codelineno-27-1" href="#__codelineno-27-1"></a>└─ bin
</span><span id="__span-27-2"><a id="__codelineno-27-2" name="__codelineno-27-2" href="#__codelineno-27-2"></a>   ├─ hong
</span><span id="__span-27-3"><a id="__codelineno-27-3" name="__codelineno-27-3" href="#__codelineno-27-3"></a>   │  └─ Person.class
</span><span id="__span-27-4"><a id="__codelineno-27-4" name="__codelineno-27-4" href="#__codelineno-27-4"></a>   │  ming
</span><span id="__span-27-5"><a id="__codelineno-27-5" name="__codelineno-27-5" href="#__codelineno-27-5"></a>   │  └─ Person.class
</span><span id="__span-27-6"><a id="__codelineno-27-6" name="__codelineno-27-6" href="#__codelineno-27-6"></a>   └─ mr
</span><span id="__span-27-7"><a id="__codelineno-27-7" name="__codelineno-27-7" href="#__codelineno-27-7"></a>      └─ jun
</span><span id="__span-27-8"><a id="__codelineno-27-8" name="__codelineno-27-8" href="#__codelineno-27-8"></a>         └─ Arrays.class
</span></code></pre></div></p>
<h4 id="_19">包作用域</h4>
<h5 id="_20">相同包</h5>
<div class="language-java highlight"><pre><span></span><code><span id="__span-28-1"><a id="__codelineno-28-1" name="__codelineno-28-1" href="#__codelineno-28-1"></a><span class="kn">package</span><span class="w"> </span><span class="nn">hello</span><span class="p">;</span>
</span><span id="__span-28-2"><a id="__codelineno-28-2" name="__codelineno-28-2" href="#__codelineno-28-2"></a>
</span><span id="__span-28-3"><a id="__codelineno-28-3" name="__codelineno-28-3" href="#__codelineno-28-3"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-28-4"><a id="__codelineno-28-4" name="__codelineno-28-4" href="#__codelineno-28-4"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-28-5"><a id="__codelineno-28-5" name="__codelineno-28-5" href="#__codelineno-28-5"></a><span class="w">        </span><span class="n">Person</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Person</span><span class="p">();</span>
</span><span id="__span-28-6"><a id="__codelineno-28-6" name="__codelineno-28-6" href="#__codelineno-28-6"></a><span class="w">        </span><span class="n">p</span><span class="p">.</span><span class="na">hello</span><span class="p">();</span><span class="w"> </span><span class="c1">// 可以调用，因为Main和Person在同一个包</span>
</span><span id="__span-28-7"><a id="__codelineno-28-7" name="__codelineno-28-7" href="#__codelineno-28-7"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-28-8"><a id="__codelineno-28-8" name="__codelineno-28-8" href="#__codelineno-28-8"></a><span class="p">}</span>
</span><span id="__span-28-9"><a id="__codelineno-28-9" name="__codelineno-28-9" href="#__codelineno-28-9"></a>
</span><span id="__span-28-10"><a id="__codelineno-28-10" name="__codelineno-28-10" href="#__codelineno-28-10"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-28-11"><a id="__codelineno-28-11" name="__codelineno-28-11" href="#__codelineno-28-11"></a><span class="w">    </span><span class="c1">// 包作用域:</span>
</span><span id="__span-28-12"><a id="__codelineno-28-12" name="__codelineno-28-12" href="#__codelineno-28-12"></a><span class="w">    </span><span class="kt">void</span><span class="w"> </span><span class="nf">hello</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-28-13"><a id="__codelineno-28-13" name="__codelineno-28-13" href="#__codelineno-28-13"></a><span class="w">        </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Hello!&quot;</span><span class="p">);</span>
</span><span id="__span-28-14"><a id="__codelineno-28-14" name="__codelineno-28-14" href="#__codelineno-28-14"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-28-15"><a id="__codelineno-28-15" name="__codelineno-28-15" href="#__codelineno-28-15"></a><span class="p">}</span>
</span></code></pre></div>
<h5 id="_21">不同包</h5>
<p>引用其他的class
第一种，直接写出完整类名，例如：
<div class="language-java highlight"><pre><span></span><code><span id="__span-29-1"><a id="__codelineno-29-1" name="__codelineno-29-1" href="#__codelineno-29-1"></a><span class="c1">// Person.java</span>
</span><span id="__span-29-2"><a id="__codelineno-29-2" name="__codelineno-29-2" href="#__codelineno-29-2"></a><span class="kn">package</span><span class="w"> </span><span class="nn">ming</span><span class="p">;</span>
</span><span id="__span-29-3"><a id="__codelineno-29-3" name="__codelineno-29-3" href="#__codelineno-29-3"></a>
</span><span id="__span-29-4"><a id="__codelineno-29-4" name="__codelineno-29-4" href="#__codelineno-29-4"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-29-5"><a id="__codelineno-29-5" name="__codelineno-29-5" href="#__codelineno-29-5"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-29-6"><a id="__codelineno-29-6" name="__codelineno-29-6" href="#__codelineno-29-6"></a><span class="w">        </span><span class="n">mr</span><span class="p">.</span><span class="na">jun</span><span class="p">.</span><span class="na">Arrays</span><span class="w"> </span><span class="n">arrays</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">mr</span><span class="p">.</span><span class="na">jun</span><span class="p">.</span><span class="na">Arrays</span><span class="p">();</span>
</span><span id="__span-29-7"><a id="__codelineno-29-7" name="__codelineno-29-7" href="#__codelineno-29-7"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-29-8"><a id="__codelineno-29-8" name="__codelineno-29-8" href="#__codelineno-29-8"></a><span class="p">}</span>
</span></code></pre></div>
很显然，每次写完整类名比较痛苦。</p>
<p>因此，第二种写法是用import语句，导入小军的Arrays，然后写简单类名：
<div class="language-java highlight"><pre><span></span><code><span id="__span-30-1"><a id="__codelineno-30-1" name="__codelineno-30-1" href="#__codelineno-30-1"></a><span class="c1">// Person.java</span>
</span><span id="__span-30-2"><a id="__codelineno-30-2" name="__codelineno-30-2" href="#__codelineno-30-2"></a><span class="kn">package</span><span class="w"> </span><span class="nn">ming</span><span class="p">;</span>
</span><span id="__span-30-3"><a id="__codelineno-30-3" name="__codelineno-30-3" href="#__codelineno-30-3"></a>
</span><span id="__span-30-4"><a id="__codelineno-30-4" name="__codelineno-30-4" href="#__codelineno-30-4"></a><span class="c1">// 导入完整类名:</span>
</span><span id="__span-30-5"><a id="__codelineno-30-5" name="__codelineno-30-5" href="#__codelineno-30-5"></a><span class="kn">import</span><span class="w"> </span><span class="nn">mr.jun.Arrays</span><span class="p">;</span><span class="c1">//import mr.jun.*;导入该类下所有包</span>
</span><span id="__span-30-6"><a id="__codelineno-30-6" name="__codelineno-30-6" href="#__codelineno-30-6"></a>
</span><span id="__span-30-7"><a id="__codelineno-30-7" name="__codelineno-30-7" href="#__codelineno-30-7"></a><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Person</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-30-8"><a id="__codelineno-30-8" name="__codelineno-30-8" href="#__codelineno-30-8"></a><span class="w">    </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">run</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-30-9"><a id="__codelineno-30-9" name="__codelineno-30-9" href="#__codelineno-30-9"></a><span class="w">        </span><span class="n">Arrays</span><span class="w"> </span><span class="n">arrays</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Arrays</span><span class="p">();</span>
</span><span id="__span-30-10"><a id="__codelineno-30-10" name="__codelineno-30-10" href="#__codelineno-30-10"></a><span class="w">    </span><span class="p">}</span>
</span><span id="__span-30-11"><a id="__codelineno-30-11" name="__codelineno-30-11" href="#__codelineno-30-11"></a><span class="p">}</span>
</span></code></pre></div>
在写import的时候，可以使用*，表示把这个包下面的所有class都导入进来（<code>但不包括子包的class</code>）</p>
<h3 id="_22">编译时多结构包编译</h3>
<h4 id="inux">inux环境</h4>
<p>首先，确保当前目录是work目录，即存放src和bin的父目录：
<div class="language-bash highlight"><pre><span></span><code><span id="__span-31-1"><a id="__codelineno-31-1" name="__codelineno-31-1" href="#__codelineno-31-1"></a>$<span class="w"> </span>ls
</span><span id="__span-31-2"><a id="__codelineno-31-2" name="__codelineno-31-2" href="#__codelineno-31-2"></a>bin<span class="w"> </span>src
</span></code></pre></div>
然后，编译src目录下的所有Java文件：
<div class="language-bash highlight"><pre><span></span><code><span id="__span-32-1"><a id="__codelineno-32-1" name="__codelineno-32-1" href="#__codelineno-32-1"></a>$<span class="w"> </span>javac<span class="w"> </span>-d<span class="w"> </span>./bin<span class="w"> </span>src/**/*.java
</span></code></pre></div>
命令行-d指定输出的class文件存放bin目录，后面的参数src/*<em>/</em>.java表示src目录下的所有.java文件，包括任意深度的子目录。</p>
<h4 id="windows">windows环境</h4>
<p>注意：Windows不支持**这种搜索全部子目录的做法，所以在Windows下编译必须依次列出所有.java文件：
<div class="language-bash highlight"><pre><span></span><code><span id="__span-33-1"><a id="__codelineno-33-1" name="__codelineno-33-1" href="#__codelineno-33-1"></a>C:<span class="se">\w</span>ork&gt;<span class="w"> </span>javac<span class="w"> </span>-d<span class="w"> </span>bin<span class="w"> </span>src<span class="se">\c</span>om<span class="se">\i</span>transwarp<span class="se">\s</span>ample<span class="se">\M</span>ain.java<span class="w"> </span>src<span class="se">\c</span>om<span class="se">\i</span>transwarp<span class="se">\w</span>orld<span class="se">\P</span>ersion.java
</span></code></pre></div>
如果编译无误，则javac命令没有任何输出。可以在bin目录下看到如下class文件：
<div class="language-text highlight"><pre><span></span><code><span id="__span-34-1"><a id="__codelineno-34-1" name="__codelineno-34-1" href="#__codelineno-34-1"></a>bin
</span><span id="__span-34-2"><a id="__codelineno-34-2" name="__codelineno-34-2" href="#__codelineno-34-2"></a>└── com
</span><span id="__span-34-3"><a id="__codelineno-34-3" name="__codelineno-34-3" href="#__codelineno-34-3"></a>    └── itranswarp
</span><span id="__span-34-4"><a id="__codelineno-34-4" name="__codelineno-34-4" href="#__codelineno-34-4"></a>        ├── sample
</span><span id="__span-34-5"><a id="__codelineno-34-5" name="__codelineno-34-5" href="#__codelineno-34-5"></a>        │   └── Main.class
</span><span id="__span-34-6"><a id="__codelineno-34-6" name="__codelineno-34-6" href="#__codelineno-34-6"></a>        └── world
</span><span id="__span-34-7"><a id="__codelineno-34-7" name="__codelineno-34-7" href="#__codelineno-34-7"></a>            └── Person.class
</span></code></pre></div>
现在，我们就可以直接运行class文件了。根据当前目录的位置确定classpath，例如，当前目录仍为work，则classpath为bin或者./bin：
<div class="language-bash highlight"><pre><span></span><code><span id="__span-35-1"><a id="__codelineno-35-1" name="__codelineno-35-1" href="#__codelineno-35-1"></a>$<span class="w"> </span>java<span class="w"> </span>-cp<span class="w"> </span>bin<span class="w"> </span>com.itranswarp.sample.Main<span class="w"> </span>
</span><span id="__span-35-2"><a id="__codelineno-35-2" name="__codelineno-35-2" href="#__codelineno-35-2"></a>Hello,<span class="w"> </span>world!
</span></code></pre></div></p>
<h3 id="_23">内部类</h3>
<p>内部类（Inner Class）是定义在另一个类内部的类。</p>
<h3 id="javabean">JavaBean</h3>
<p>JavaBean是一种符合<code>命名规范的class</code>，它通过getter和setter来定义属性；</p>
<p>属性是一种通用的叫法，并非Java语法规定；</p>
<p>可以利用IDE快速生成getter和setter；</p>
<p>使用Introspector.getBeanInfo()可以获取属性列表。</p>












                
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